// Mgmt
// Copyright (C) 2013-2019+ James Shubin and the project contributors
// Written by James Shubin <james@shubin.ca> and the project contributors
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package coredatetime

import (
	"time"

	"github.com/purpleidea/mgmt/lang/funcs/facts"
	"github.com/purpleidea/mgmt/lang/types"
)

func init() {
	facts.ModuleRegister(ModuleName, "now", func() facts.Fact { return &DateTimeFact{} }) // must register the fact and name
}

// DateTimeFact is a fact which returns the current date and time.
type DateTimeFact struct {
	init      *facts.Init
	closeChan chan struct{}
}

// Validate makes sure we've built our struct properly. It is usually unused for
// normal facts that users can use directly.
//func (obj *DateTimeFact) Validate() error {
//	return nil
//}

// Info returns some static info about itself.
func (obj *DateTimeFact) Info() *facts.Info {
	return &facts.Info{
		Output: types.NewType("int"),
	}
}

// Init runs some startup code for this fact.
func (obj *DateTimeFact) Init(init *facts.Init) error {
	obj.init = init
	obj.closeChan = make(chan struct{})
	return nil
}

// Stream returns the changing values that this fact has over time.
func (obj *DateTimeFact) Stream() error {
	defer close(obj.init.Output) // always signal when we're done
	// XXX: this might be an interesting fact to write because:
	// 1) will the sleeps from the ticker be in sync with the second ticker?
	// 2) if we care about a less precise interval (eg: minute changes) can
	// we set this up so it doesn't tick as often? -- Yes (make this a function or create a limit function to wrap this)
	// 3) is it best to have a delta timer that wakes up before it's needed
	// and calculates how much longer to sleep for?
	ticker := time.NewTicker(time.Duration(1) * time.Second)

	// streams must generate an initial event on startup
	startChan := make(chan struct{}) // start signal
	close(startChan)                 // kick it off!
	defer ticker.Stop()
	for {
		select {
		case <-startChan: // kick the loop once at start
			startChan = nil // disable
		case <-ticker.C: // received the timer event
			// pass
		case <-obj.closeChan:
			return nil
		}

		select {
		case obj.init.Output <- &types.IntValue{ // seconds since 1970...
			V: time.Now().Unix(), // .UTC() not necessary
		}:
		case <-obj.closeChan:
			return nil
		}
	}
}

// Close runs some shutdown code for this fact and turns off the stream.
func (obj *DateTimeFact) Close() error {
	close(obj.closeChan)
	return nil
}